Haemorrhagic smolt syndrome: a severe anaemic condition in farmed salmon in Scotland.

Farmed pre-smolt stage Atlantic salmon developed an acute, severe haemorrhagic anaemia, termed haemorrhagic smolt syndrome. The fish were in good condition, but lethargic, and had widespread visceral and muscle petechiation and ecchymoses. The mean (sd) haematocrit of affected fish was 1.4(0.9) per cent and histopathology revealed widespread haemorrhage in all organs, associated with endothelial tissue. No infectious agent was isolated and the condition could not be transmitted experimentally. The clinical evidence indicates that the condition is non-infectious, but its aetiology could not be fully established.